First of all, the *.opt file has nothing to do with the password.
This file simply stores the user defined options, things like fonts, colours, toolbar layout etc.

If you have the laptop (with the original program in), simply open the project, open the PLC properties from the pop-up menu, (right click the PLC in the project workspace) and there (under the tab marked 'protection') will be the password.
If you don't have the program, I'm afraid to say that there is no way to retrieve the password from the PLC itself.